Coexistence of two different energy transfer processes in SiO2 films containing Si nanocrystals and Er

Abstract

The mechanism of energy transfer from silicon nanocrystals (nc-Si) to erbium ions $({\mathrm{Er}}^{\text{3+}})$ in ${\mathrm{SiO}}_2$ films containing nc-Si and Er was studied by analyzing delayed infrared luminescence from ${\mathrm{Er}}^{\text{3+}}.$ It was found that, to theoretically reproduce the rising part of the time-dependent luminescence intensity, two different energy transfer processes, i.e., fast and slow processes, should be considered. From the fitting of the delayed luminescence to a model, the ratio of the two energy transfer processes and the energy transfer rate of the slow process were estimated. The ratio exhibited a clear dependence on the luminescence peak energy of Si nanocrystals, which act as photosensitizers for ${\mathrm{Er}}^{\text{3+}},$ indicating that the ratio depends on the size of nc-Si. The ratio of slow to fast processes increased with the decrease in size; this observation is a strong indication that the fast process is the direct inheritance of the process in bulk Si:Er systems, and the slow process is a characteristic process occurring only in nc-Si:Er systems. The energy transfer rate of the slow process was found to depend on the recombination rate of excitons in nc-Si.